There are 3 primary objectives in the project: 1) to localize brain structure that may be involved in the etiology and pathophysiology of TS and OCD; 2) to identify the neurobiological mechanisms particularly neuropsychological mechanisms that mediate these etiologically related disorders of childhood onset; and, 3) to determine the extent to which specific environmental exposures my affect the emergence of tics and/or obsessive compulsive systems.